In a liquid crystal panel, a display side substrate (front side substrate) and a liquid crystal driving side substrate (rear side substrate) are faced with each other and a liquid crystal compound is filled and sealed between these substrates to form a thin liquid crystal layer. The liquid crystalline alignment in the liquid crystal layer is electrically controlled through the liquid crystal driving side substrate to selectively change the amount of light transmitted through the display side substrate or light reflected thereon, thereby performing display.
For a liquid crystal panel, various driving systems are known, examples of which include a static driving system, a simple matrix system, and an active matrix system. In recent years, color liquid crystal display devices using a liquid crystal panel according to an active matrix system or a simple matrix system have spread rapidly as flat displays for personal computers, portable information terminals and so on.
FIG. 1 illustrates an example of a liquid crystal panel according to an active matrix system. A liquid crystal panel 101 has a structure wherein a color filter 1, which is a display side substrate, is faced with a TFT array substrate 2, which is a liquid crystal driving side substrate, to form a gap part 3 of about 1 to 10 μm; the gap 3 is filled with a liquid crystal L; and the periphery thereof is sealed up with a sealant 4. The color filter 1 has a structure including a black matrix layer 6 formed in a predetermined pattern for shading light from the boundary part between the pixels, a color layer 7 with a plurality of colors (in general, the three primary colors of red (R), green (G), and blue (B)) arranged in a predetermined order for forming each pixel or, recently, a color layer using a hologram, a protective film 8, and a transparent electrode film 9 successively laminated on a transparent substrate 5 in this order from the side close to the transparent substrate. On the other hand, the TFT array substrate 2 has a structure wherein TFT elements are arranged on the transparent substrate and the transparent electrode film is disposed (not illustrated). Moreover, an alignment film 10 is provided, respectively, on both inner surface sides of the color filter 1 and the TFT array substrate 2 facing thereto. Furthermore, spherical or rod-like particles 11, which have a constant size and are made of glass, alumina, a plastic or the like, are dispersed as spacers in the gap part 3 for constantly and homogeneously maintaining the cell gap between the color filter 1 and the electrode substrate 2. A color image can be obtained by controlling the light transmittance of the pixels colored in respective colors or the liquid crystal layer behind the color filter.
The protective film 8 formed in the color filter has both functions for planarizing the color filter and for protecting the color layer when a color layer is provided in the color filter. In a color liquid crystal display device, when the flatness of the transparent electrode film 9 deteriorates due to the existence of gap unevenness derived from waviness on the surface of the transparent substrate of the color filter, gap unevenness among the R, G and B pixels, or gap unevenness within each pixel, color irregularity or contrast irregularity is generated so as to give rise to a problem of image quality deterioration. Therefore, a high flatness is required for the protective film.
In the case that the fine particles 11 as shown in FIG. 1 are dispersed as the spacers, the particles 11 are randomly dispersed whether they are behind the black matrix layer 6 or behind the pixels. In the case that the particles 11 are disposed behind the display region, that is, behind the color layer, a back lighting beam transmits through the particle 11 part and further the orientation of the liquid crystal is disturbed in the vicinity of the particles 11. As a result, the display image quality is remarkably deteriorated. Thus, as shown in FIG. 2, instead of dispersing the particles 11, column-shaped spacers 12 having a height corresponding to the cell gap are formed on the inner surface side of the color filter and in the region correspondingly to the positions where the black matrix layer 6 is formed (namely, non-display region).
The color layer 7, the protective film 8 and the column-shaped spacers 12 can be made of a resin. The color layer 7 is required to be formed in a predetermined pattern for each color pixel. Considering the adhesion property and the sealing property of the sealing part, the protective film 8 is preferably one capable of covering only the region of the transparent substrate with the color layer formed thereon. Moreover, the column-shaped spacers 12 are required to be formed accurately in the region where the black matrix layer 6 is formed, that is, in the non-display region. Therefore, it is proposed that the color layer 7, the protective film 8 and the column-shaped spacers 12 are formed with the use of a photosensitive composition which can be alkali-developed after regions to be cured is selectively exposed to light.
In recent years, an increase in the area of liquid crystal display devices have been advancing, and the necessity that their cell gap should be kept even over the whole of their wide substrate has been becoming larger. When the area of the substrate is large, the substrate is distorted even by a relatively small external force. Therefore, the necessity that the unevenness of the gap based on such a distortion should be prevented has also been generated. In recent years, the thickness of the liquid crystal layer, that is, the cell gap has become smaller in order to improve display responsibility. Thus, the necessity that the small gap should be precisely maintained has also been generated.
Furthermore, in recent years, in order to remove a heating process and a slow cooling process from the process for assembling a color filter and a TFT array substrate (cell bonding) so as to make the process simpler and improve productivity, a method of performing cell bonding at a room temperature (room-temperature cell bonding method) has been proposed (Hiroyuki Kamiya et al., “Development of One Drop Fill Technology for AM-LCDs”, SID 01 DIGEST, 56.3, p. 1354-1357).
Furthermore, in order to improve the productivity of the cell bonding process, a One Drop Fill Technology (ODF technique) is proposed. In this method, a predetermined amount of a liquid crystal droplet is dropped into a liquid crystal sealing face of a liquid crystal panel substrate such as a color filter or a TFT array substrate, and another liquid crystal panel substrate is opposed and adhered thereto in a vacuum in the state that a predetermined cell gap can be kept. This method can make the processes thereof simpler than any conventional cell bonding process. According to any conventional cell bonding process, a color filter and a TFT array substrate are opposed and adhered to each other in the state that a predetermined cell gap can be kept, and subsequently a liquid crystal is filled and sealed into the cell gap via a filling-opening made in an end of the adhesion product, using a capillary phenomenon and a pressure difference between inside and outside of the cell gap. Following the above-mentioned increase in the display region and the reduction in the cell gap, it has been becoming difficult that the liquid crystal is smoothly filled into the gap. On the other hand, according to the ODF technology, a liquid crystal is easily filled into a cell gap even if the area of a liquid crystal panel substrate becomes large and its cell gap is narrow. This new method, which is superior in productivity, may become the main current hereafter.
Thus, along with recent advances of expanding the display area and narrowing the cell gap of the liquid crystal display device, only a slight failure in the uniformity or evenness of the cell gap greatly affects on the display performance, and thereby is apt to cause a deterioration of the display quality such as the display unevenness. Therefore, a request for the accurate and uniform cell gap is becoming more severe. For this reason, there is an increasing demand for forming and maintaining the cell gap with column-shaped spacers, accurately, precisely and uniformly.
Patterning layers of the color filter such as a color layer, a protective film and column-shaped spacers can be formed by forming a coating film of a photocurable resin composition on a substrate, and selectively exposing with light a desired region to be cured, and then alkali-developing, and further curing by heating or the like.
As the photocurable resin compatible for the alkali development, a composition in which a polyfunctional acryl monomer and a photopolymerization initiator are compounded in an alkali soluble binder can be used.
Japanese Patent Application Laid-Open No. 2000-105456 discloses a copolymer suitable for an alkali soluble binder, which has an alkali soluble carboxyl group and a radical polymerizing (meth)acryloyl group and has a photocurability per se.
In the case that the color layer such as pixel and black matrix is formed by using the photocurable resin composition compatible for the alkali development, a higher color concentration can be obtained by increasing the content ratio of the colorant. In the case that a pigment is used as the colorant, the content ratio of a pigment dispersing agent also increases. As well, if the content ratio of the photopolymerization initiator is increased, the sensitivity of the photocurable resin increases, so that it can be cured for a short time with less light exposure. However, if the content ratio of the colorant, the dispersing agent and/or the photopolymerization initiator and the like is high, the content ratio of the alkali soluble binder decreases. Thereby, the curability, the alkali developing property of the resin, and the shape after development and the like deteriorate.
If a polyfunctional monomer is compounded in the photocurable resin in accordance with an increase of the colorant, the curability increase, and the sensitivity, the hardness, the strength, the adhesiveness and the like of the color pattern are improved. However, compounding or increasing the polyfunctional monomer further decreases the content ratio of the alkali soluble binder. Thereby, the developing property of the photocurable resin further deteriorates. If the alkali developing property of the photocurable resin deteriorates, various problems become noticeable, such as the deterioration of the pattern edge shape, the formation of the inverse tapered shape, the elongation of the developing time, the residue on the exposed surface via the development of the substrate and so on.
On the other hand, the polymerization initiator having the tertiary amine structure in its molecule is very effective as a polymerization initiator, because the tertiary amine structure part acts as an oxygen quencher, so that a radical generated from the polymerization initiator is not likely to be deactivated by oxygen. However, if the content of this initiator is excessively increased in order to improve the sensitivity, the amount of the alkali soluble binder and the polyfunctional monomer decreases relatively in the composition. This may cause deterioration in the curability such as the hardness or strength after curing, or in the alkali developing property such as the developing speed, the plate making property (pattern accuracy) and residue.
In the case that a large amount of the polymerization initiator having the tertiary amine structure in its molecule is mixed with the copolymer disclosed in the aforementioned Japanese Patent Application Laid-Open No. 2000-105456, another problem arises in addition to the above problems. That is, in this case, the tertiary amine structure coordinates with a carboxyl group of the copolymer, and the acidity and the alkali solubility of the copolymer decreases. Thereby, a superior alkali developing property of the copolymer having the carboxyl group and the (meth)acryloyl group cannot be fully exerted. If it is contemplated compensating the alkali developing property of the copolymer itself, taking into account increasing the amount of the polymerization initiator having the tertiary amine, another problem may arise. That is, if the amount of the carboxyl group to be incorporated into the copolymer increases, the solubility of the binder in the solvent decreases.
On the other hand, Japanese Patent Application Laid-Open No. 2001-91954 discloses a photosensitive composition for column-shaped spacers which is a photosensitive composition mainly comprising resin, monomer, photopolymerization initiator and solvent, and characterized in that a specific structured polyfunctional acryl monomer having a carboxyl group and a specific structured polyfunctional acryl monomer having no carboxyl group are contained as the monomer. In Japanese Patent Application Laid-Open No. 2001-91954, it is contemplated improving the developing property when the column-shaped spacers are formed, by using a monomer represented by the following formula (101), and contemplated improving the adhesiveness between the column-shaped spacers and a glass substrate by using a monomer represented by the following formula (102).

However, it cannot be said that the alkali developing property is sufficient even in the case of the photosensitive composition disclosed in Japanese Patent Application Laid-Open No. 2001-91954
Meanwhile, the liquid crystal display device today becomes more advanced in their image quality and resolution. Along with this, display pixels become finer, and the concentration of the pigment to be contained in the color filter (color layer) becomes higher.
In order to obtain the liquid crystal display device with a high image quality and a high resolution, individual pixels are required to be finer, while the displacement of the column-shaped spacer and the color layer, respectively, in the liquid crystal panel is prevented, and the cell gap unevenness is prevented as much as possible. For this purpose, it is required that both a patterning accuracy during formation of the column-shaped spacers and a patterning accuracy during formation of the color layer are improved, and the strength of the column-shaped spacers is improved.
The strength of the column-shaped spacers can be improved by increasing the amount of the monomer (including oligomers) to be used as a material thereof in the photosensitive composition, and thereby increasing the cross-link density. However, along with the increase of the monomer amount to be used, typically deterioration arises in the alkali developing property after selectively exposing with light the coating film made of the photosensitive composition by a photolithography or the like, for example.
As well, the concentration of the pigment to be contained in the color layer can be increased, by increasing the amount of the dispersing agent to be used. However; in the case of amine dispersing agent which is often used as a dispersing agent, along with the increase of the amount to be used, typically deterioration arises in the alkali developing property of the coating film made of the photosensitive composition (with the pigment dispersed).
The deterioration in the alkali developing property causes deterioration in the patterning accuracy. This is a factor of deteriorating the positioning accuracy and the shape accuracy of the color layer or the column-shaped spacers. As the result, this causes a reduction of the yield ratio, when a liquid crystal display device with a high image quality and a high resolution is produced.